What's wrong with existing systems?

Very few systems offer variable airflow control, usual way of operating is known as "bang-bang" - totally open or totally closed damper. The consequences of this are the temperature swing (common for all low to midrange HVAC systems, though), abrupt changes of the airflow and static pressure, and associated noise.

The extensibility of the zoning systems is usually very poor - "advanced" systems that are capable of handling just 2-3 zones are not a rarity.

All of the systems offered on the market are proprietary.

How is Home Climate Control better than commercially available systems?

Previous paragraph points out what's wrong with existing systems.

Now, here's why it's wrong. Existing systems were built by companies that have been on the market for a long time, have established operating procedures, trained personnel, quite possibly they have grown beyond the ability to change. They do stuff a certain way "because we always did it this way". They completely ignore the progress in the embedded systems and still rely on low integration specialized chips to manufacture their controllers, and miss the opportunity to utilize the power that embedded microprosessor based systems offer.

This system, on the other hand, was originally created as a hobby project that was not intended to be run on anything other than a quite powerful workstation, but in the end it turned out that it is SO SIMPLE, it can be run on $100 microprocessor board without any changes to it.

Summarizing the advantages:

It is infinitely flexible;

The number of zones is practically unlimited;

Functionality can be added without adding cost;

It can work with cheap hardware as well as expensive without any changes;

It can be remotely controlled;

It can be remotely diagnosed;

It is fault tolerant;

It is cheap as dirt.

How many zones can the system control?

Short answer: unlimited.

Long answer: it is limited by how many damper controllers you can connect to your computer. If you use the serial controller, the reasonable number is one (or two, if you use the USB controller for 1-Wire® network devices). If the servo controller is stackable, the reasonable practical limit is somewhere between 128 and 256. If the servo controller is a USB device, you can install up to 256 servo controllers (less number of USB hubs), each of them supports 4 to 8 dampers.

Can the system be used for gas heating?

Clarification: this question pertains to forced air gas heater, also known as a furnace.

Yes, in fact it works even better with gas heating because the heat exchanger takes time to cool down after the gas valve has been closed allowing the gas valve to be cycled to maintain a constant discharge temperature. The controller will prevent the heat exchanger from overheating while the unit safeties will remain in case of a catastrophic failure.

Can the system be used for water heating?

Clarification: this question pertains to the heater that heats the water in the tank and then sends it to heat the radiators in the rooms.

Tough question.

From the technical standpoint, there's nothing preventing the system to do so - all you have to do is to use the computer controlled valves and a different driver for the heater.

From the safety standpoint, the consequences of the water heater system gone amok are far greater than for the forced air system - anyone in vicinity of the exploding hot water pipe is guaranteed to have at least severe burns. On the positive side, water heaters usually have advanced safeguards preventing this from happening even in case of grave user mistakes.

Update: starting about December 2003 the system is, in fact, being successfully used to control the water boiler.

Can the system be used for radiant heating?

Several attempts to do that are currently happening. One of them is being publicly documented, in Hungarian, though :)

Is it possible to have a wall controller?

Short answer: yes.

Long answer: it depends on how much you are willing to spend. A single wall controller for all the zones will cost about $150-200, which is comparable or less than "professionally istalled" one, a simple room controller will cost much less, but it was not spec'd yet.

Ask yourself a question: do you really need a wall controller? How often do you use your TV's control panel? All of them now come with remotes...

Update (2009/11): Wall controller will be most probably abandoned in favor of Android based application.

What's wrong with making the graphs visible to all the Internet?

Call me paranoid, but this can be used by someone with malicious intent to figure out your schedule, whether you're home or not, and even what room people are in at any given moment of time.